Marine stern rudder blade

ABSTRACT

A single blade stern rudder having divergent side wall surfaces near the trailing edge to provide the part of the rudder blade of maximum cross-sectional width near the rudder trailing edge and remote from the rudder pivot axis. Such a rudder may be of the partly-balanced type without a stationary stern post and may have a divergent-convergent cross-section away from the said divergent side wall surface region.

United States Patent 11 1 Kaufer 1 Nov. 12, 1974 1 MARINE STERN RUDDER BLADE 22 Filed: Dec. 12, 1972 21 Appl. No.: 314,447

[30] Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS 1,07l 68O 6/1967 Great Britain f. 114/162 316971 4/1934 Italy 1. 114/162 446921 5/1936 Great Britain 1 14/162 Primary ExaminerTrygve M. Blix Assistant E.\'aminerStuart M. Goldstein Attorney, Agent, or Firm-Spencer & Kaye [57] ABSTRACT A single blade stern rudder having divergent side wall surfaces near the trailing edge to provide the part of the rudder blade of maximum cross-sectional width near the rudder trailing edge and remote from the rudder pivot axis. Such a rudder may be of the partlybalanced type without a stationary stern post and may have a divergent-convergent cross-section away from the said divergent side wall surface region.

13 Claims, 6 Drawing Figures Dec. 17. 1971 Germany 2162648 July 14 1972 Germany 2234603 Nov 2, 1972 Germany 2253571 [52] [1.5. CI. 114/162 [51] Int. Cl B6311 25/06 8 Field of Search 114/162-167, 1 14/170 [56] References Cited UNITED STATES PATENTS 2 800 150 7/1957 Farwell 114/166 PATENTEDNUV 12 I914 ale-41.104 SHEET MF 3 MARINE STERN RUDDER BLADE The invention relates to a single-bladed stern rudder to be disposed rearwardly of the screw of a vessel, more particularly an inland water vessel.

Especially in inland water vessels the main function of the stern rudder consists in ensuring as small as possible a turning circle in order to enable even vessels of considerable length to be used on inland waterways which are sometimes very narrow.

A conventional single blade rudder has a crosssection substantially ofthe configuration of an elongate tear drop. The cross-section of this rudder converges gradually towards the tail end from the region of its greatest width. However, in the trailing part of the rudder the sidewalls of the rudder blade diverge again over a limited region of the length of the rudder, so that the cross-section of the rudder exhibits a broadened tail region. However, in order to pressure the stream-lined shape of the rudder and to maintain low rudder drag, this broadened portion is considerably narrower than the maximum cross-sectional width of the rudder in the region of the bulge at the front.

The improvement of maneuverability of vessels obtained with this rudder was evidently very slight or unsatisfactory. Although this proposal dates back to the year 1934 it has not been accepted as a practical construction. Instead the practice for improving manoeuvrability of vessels proceeded along different lines.

One of these alternative developments used a rudder blade divided into two blade portions disposed in series pivoted to one another such that the trailing part can be set at a greater angle of attack to the flow of water than is the leading end. This solution has certain drawbacks of construction and of the design of the rudder drive mechanism.

Other proposals have involved replacing the singlebladed rudder arranged rearwardly of the screw tunnel by a multi-blade rudder consisting ofa plurality ofjuxtaposed, staggered and correspondingly smaller rudder surfaces. The steering effect, when travelling along curved paths, is no doubt more favorable than with the conventional single-blade rudder, but the cost of construction of the rudder drive mechanism is correspondingly high. This solution is therefore only recommended for vessels where the additional expense is not of paramount importance. For simple cargo vessels for inland navigation such equipment is too costly, particularly bearing in mind the risk of damage by running aground at sloping embankments or banks.

The present invention is based on the problem of designing a single-blade stern rudder in such a manner as thereby to obtain a manoeuvrability superior to that obtainable with the known rudders.

According to the present invention there is provided a marine single-blade stern rudder including means to receive a pivot shaft, side wall surfaces divergent away from the pivot shaft mounting to give the rudder its maximum cross-sectional width at a location remote from the pivot shaft mounting. The shape of the rudder upstream of the diverging sidewall surfaces is, in principle, not of decisive importance to the appreciably enhanced maneuverability. For example, it may have the conventional shape of an elongate tear drop. The crosssection of the rudder blade may also gradually widen from head to tail end. It has proved particularly advantageous and suitable, with regard to the constructional requirements of the rudder drive mechanism, for the rudder blade as viewed in the flow direction to have upstream of the divergent side wall surfaces a divergent convergent cross-sectional configuration resembling that of an athletes discus and having at either side ends which taper in longitudinal direction from a median region.

The present invention provides an amazingly simple solution to the problem of marine craft manoeuvrability as has been established by experiments comparing the presently proposed rudder with the known form of single blade stern rudder having slightly divergent portions as mentioned above. British Patent Specification No. 446,921 shows that the hydrodynamic flow (known from aerofoil theory) forms about therudder and closely follows the rudder surface, except for the boundary layer. A comparatively slight widening of the cross-section, designated by the reference numeral 7 in the said specification No. 446,921, opposes the generally tailward directed flow. However, the flow does not adapt itself to this wider portion but forms instead a stationary eddy at the transition between the divergent sidewall portion and the adjoining surface portions, rather like that illustrated in FIG. I61 of the textbook Technische Stroemungslehre by Eck published in 1941. The current appears to slide over this stationary eddy and thus in the region of the eddy there can be no component of force generated to assist the rudder action. On the other hand, in the subject of the invention no such stationary eddy forms in the rearward region of the rudder, as viewed in flow direction, with the result that the hydrodynamic flow follows closely the divergent sidewall surfaces at the trailing part of the rudder blade to provide a more effective deflection of the screw wash.

It has also proved advantageous for a sharp transition to be provided between the broadened cross-section region and the main rudder blade region.

The rudder of the present invention is particularly effective when, upon a rudder deflection, all or most of the water flow produced by the screw engages that face of the rudder which is to'be pressurized. To this end it is contemplated that the ratio of the length of rudder trailing part behind the pivot shaft axis to that of the leading part ahead of the pivot axis be smaller than 2:1.

Furthermore, provision should advantageously be made for the greatest possible volume of the current produced by the screw to glide along the pressurized side of the rudder blade from leading edge to trailing edge. This is not necessarily the case when the leading edge of the rudder facing the screw is rounded, since then this edge forms a smooth guidance surface for the screw wash and hence a part of the moving water will run off without producing any effect on the rudder. It

is even possible for such a rounded leading edge to gen-' erate a component of force actingcounter to the intended direction of steering. In order to reduce appreciably such a loss of current over the leading edge of the rudder, the leading edge may suitably be designed as a cutting edge, but this does not, of course, means as sharp as a knife. The edge should onlybe of a width considerably less than the mean width of the remainder of the rudder blade so as to act like a cutting edge in comparison to the maximum width of the rudder, and so as to form a substantially increased resistance to flow when the sharp edged rudder is deflected. More suitably the leading edge of the rudder may be in the form of a strip of sheet metal extending in the direction of the longitudinal plane of the rudder.

As viewed in flow direction, the cross-sectional widening of the tail end may terminate in two surfaces convergent along the flow direction. However, the divergent surface portions may very simply be formed by two free plates projecting outwardly. The plates may be welded to the rudder blade by their edge adjoining the latter. alternatively gaps may be left to serve as throughflow slots between web plate and rudder blade, through which slots part of the wash from the screw can flow without hindrance when the vessel is under way on a straight course. The web plates may have an aerofoil cross-section so as to reduce the flow resistances especially in straight ahead travel.

Advantageously the rudder blade may have, above and below the vertical extent of the screw, flow-guiding plates each extendng longitudinally of the rudder blade at either side of the sidewalls of the rudder and jutting out therefrom, for the purpose of forming respective channels of enforced flow of the screw wash. It is thereby ensured that the screw wash does not escape upwardly or downwardly but is confined to pass along the rudder bladesurface over all of its length. It is more particularly contemplated for the flow-guiding plates to extend substantially horizontally. A structurally advantageous embodiment provides for upper and lower edges of the lateral surface portions of the divergent plates to extend at least as far as the flow-guiding plates and optionally to be secured thereto.

In order that the presentinvention may more readily be understood the following description is given, merely by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 shows a side view of the rudder with the ships,

stern represented schematically;

FIG. 2 shows a plan view of the rudder along line 11-11 of FIG. 1;

FIG. 3 corresponds to FIG. 2 but shows a modified embodiment of the rudder;

FIG. 4 shows a furtherembodiment of the rudder according to the invention;

FIGS shows a section along line VV of FIG. 4, and

FIG. 6 is an illustration of the mode of operation of the rudder of FIGS. 1 and 2.

The rudder shaft 3 of the rudder 4 is rotatably mounted in the stem 1 of the body of the vessel generally designated by the reference numeral 2. The screw tunnel is located in the bottom of the stem 1 and the ships screw 7 is rotatably mounted within the screw tunnel 5 on the shaft 5 indicated schematically by broken lines. The stem rudder 4 is located at the level of the screw and directly astern of the screw 7 in the flow direction 8, and there is no stationary stern post disposed between the rudder leading edge and the propulsion screw, the rudder shaft 3 being shrouded by the rudder blade itself.

The leading part of the rudder ahead of the shaft 11 is designated 9 and the trailing part behind the shaft 11 by the numeral 10. The ratio of length 13 of the trailing part to the length 14 of the leading part 9, both measured along the flow direction 8, is less than 2 f 1. This means that the pivot axis 11 is spaced from the rudder leading edge by more than 33 percent of the total rudder length and is disposed almost in the middle of the rudder. In conventional rudders the corresponding ratio of lengths is more than 2 1, i.e. thepivot axis 11 is arranged nearer the leading edge of the rudder 4.

Thetrailing part 10 of the rudder is in turn subdivided into a front portion 160 and a rear portion 16. Up to the imaginary dividing line 17 between front portion 16a and rear portion 16 of the rudder trailing part 10, the rudder has, when viewed in flow direction, substantially the cross-sectional configuration of an ath- Ietes discus with ends tapering outwardly in the longitudinal direction to either side of the pivot axis 11. In the rear portion 16 of the trailing part 10 the sidewalls 18, 19 first diverge as seen in the flow direction 8. At the extremity of the divergent portion of the side walls l8, 19 the sidewalls have a spacing 20 from one another which is greater tan the cross-sectional width 21 of the rudder blade in its actual middle zone on the axis of the shaft 11. The transitions between the front portion 16a and rear portion 16 of the trailing part 10, in the region of the imaginary dividing line 17, are in the form ofa sharp line kink.

The extreme leading edge 15 of the rudder leading portionis formed in the manner ofa cutting edge. More particularly, this edge is formed by a sheet metal portion extending in a direction parallel to the axis of the rudder shaft 11 and lying in the central longitudinal vertical plane of the rudder 4 as FIGS. 1 and 2 indicate.

each of aerofoil section with outwardly situated tail ends. The cross-sectional outline of each plate, as it may be well observed in FIG. 4, has a rearwardly tapering outline.

The rudder blade 4 is also provided with a flowguiding plate 30 below the vertical extent 29 of the screw 7 and a pair of such plates 31, 32 above the screw extent. These plates 30, 31, 32, in this case formed of sheet metal, are disposed transversely to the axis of the rudder pivot shaft 3 to extend in the longitudinal direction of the rudder blade (flow direction 8) and jut out at either side from the sidewalls of the rudder blade. In this way flow passages 33, 34 confine'the screw wash against escaping the influence of the rudder by migration upwardly or downwardly.

The rudder blade is formed of metal sheets joined by welding or rivetting, as is illustratively indicated in the various Figures. The metal sheets form the sidewalls of the rudder blade.

The rudder according to the invention was tested in a vessel having a load capacity of 1,500 tons. The length of the vessel was m, its width 9.0 m andthe lateral elevation 2.90 m. The leading edge 15 of the rudder was spaced 200 mm. from the plane of rotation of the screw 7. The length 14 of the rudder leading part, measured along the flow direction, amounted to 1,000 mm. and the corresponding length 13 of the trailing part was 1,270 mm. The distance between the axis of the rudder pivot shaft 11 and the region 20 of maxium width at the rear portion 16 of the tail amounted to 1,060 mm. Thus the pivot axis was situated substantially halfway between the leading edge and the region of maximum width of the rear portion of the rudder trailing part. The rudder had a height of 2,050 mm. The surface area of the rudder leading part amounted to 37.25 percent of the overall area of the rudder. For reasons of construction the side elevation of the rudder was not rectangular or square but was recessed at 35 in the region of its upper edge facing the screw tunnel to conform to the configuration of the stern of the vessel.

The mode of operation of the rudder according to the invention is illustrated in FIG. 6 with reference to the rudder of FIG 2, but it is analogous to the operation mode of all rudders according to the invention.

The shape of the rear portion 16 of the rudder causes, in the extreme hard-about position a second deflection of the screw wash stream which has already been engaged and diverted by the forward portion 15 and the leading part 9 of the rudder. Moreover, the relatively sharp leading edge ensures that if, for example, the rudder is turned to starboard the tendency for the screw wash to be diverted to port is hardly noticeable as compared to the effect of known rudders. Beyond a specific angle of deflection a the rudder embraces the entire screw wash and diverts it in such manner that the flow direction of the reflected wash has a major component running precisely transversely of the vessel and even has a further component directed toward the bow (angle [3).

As set forth earlier, a superior maneuverability of the ship is achieved according to the invention, if the rudder receives and thus deflects the entire screw wash when the rudder is in an extreme or hard-aboutT position and subsequently a second deflection of the screw wash is effected by one of the divergent surfaces 18 or 19. The geometrical arrangement between the rudder 4 and the ship screw 7 for achieving these results can be seen upon observing together the side elevational view of FIG. 1 and the plan view of FIG. 6.

Thus, to enable the rudder 4 to receive the entire screw wash, the imaginary projection of the rotational outline (that is, the circumscribed circle) of the screw 7 onto the rudder 4 should be within the combined area of the leading part 9 and the front portion 16a of the trailing part 10, when the rudder 4 is in a hard-about position. This will be accomplished if, with a centered arrangement of the rudder 4 with respect to the ship screw 7, the leading part 9 and the front portion 16a of the trailing part 10 of the rudder each has a horizontally measured length which is at least as large as the radius of the screw 7. These relative dimensions are clearly observable in FIG. 6.

As it is further seen in FIG. 6, the aforenoted second deflection of the screw wash is particularly ensured if, in the hard-about position of the rudder 4, the divergent surfaces 18 and 19 lie substantially outside the rotational outline of the screw 7 projected onto the rudder 4. This will be accomplished if as it is also well observable in FIGS. 2 and 6 the divergent wall surfaces 18 and 19 are spaced from the pivot axis 11 at a distance that is greater than the radius of the screw '7.

I claimf l. A single-blade rudder secured to the stern ofa ship for motion about a vertical pivot axis into opposite extreme or hard-about positions, the ship having a screw that generates a screw wash extending parallel to the forward direction of straight-line travel of the ship, the screw having a radius and a rotational outline, the rudder being situated in its entirety rearwardly of said screw in central alignment therewith, comprising in combination:

a. a leading part extending from said pivot axis for-' wardly thereof and having. a horizontally measured length dimension at least as large as the screw radius; and

b. a trailing part extending from said pivot axis rearwardly thereof, said trailing part having I. a front portion extending from said pivot axis rearwardly thereof and having a horizontally measured length dimension at least as large as the screw radius, whereby a projection of said rotational outline of said screw onto said rudder parallel to said direction is substantially fully within the combined area of said leading part and said front portion of said trailing part in either extreme position of the rudder for receiving the entire screw wash, said leading part and said front portion of said trailing part effecting a first deflection of the screw wash;

2. a rear portion adjoining a rear terminus of said front portion and extending rearwardly thereof, said rear portion including rearwardly divergent lateral wall surfaces foreffecting a second deflection of the screw wash subsequent to its said first deflection when said rudder is in either of its extreme positions.

2. A rudder as defined in claim 1, wherein said divergent wall surfaces of said rear portion are spaced from said pivot axis at a distance that is greater than said screw radius, whereby said divergent wall surfaces of said rear portion are situated externally of said projection of said screw outline when said rudder is in either of said extreme positions.

3. A rudder as defined in claim 1, wherein the horizontally measured maximum distance between said divergent lateral wall surfaces constitutes the horizontally measured maximum cross-sectional width of the entire rudder.

4. A rudder as defined in claim I, wherein said leading part is formed of rearwardly divergent vertical wall surfaces, said front portion of said trailing part is formed of rearwardly convergent vertical wall surfaces.

5. A rudder as defined in claim 1, wherein the ratio of the length dimension of said trailing part to the length dimension of said leading part is smaller than 2:1, said length dimensions are horizontally measured.

8. A rudder as defined in claim 1, wherein each of said divergent wall surfaces of said rear portion is formed by a free web plate.

9. A rudder as defined in claim 8, wherein said web plates have an airfoil cross section with a rearwardly tapering outline.

10. A rudder as defined in claim 8, including means defining throughflow slots between said outwardly projecting plates and said blade. 11. A rudder as defined in claim 1, including flowguiding plate means extending laterally outwardly to either side of the rudder in planes transverse to said pivot axis, said flow-guiding plate means intersect said divergent wall surfaces of said rear portion, whereby in use of the rudder the screw wash is confined against movement clear of the influence of the rudder in a vertical direction.

12. A rudder as defined in claim 11, wherein said flow-guiding plate means extend in two vertically spaced planes each lying externally of said projection of said outline, said divergent wail surfaces of said rear portion are formed by free web plates projecting outwardly of the rudder blade and secured to said flowguiding plate means.

13. A marine single blade stern rudder comprising a rudder blade having leading and trailing parts, means for receiving a pivot shaft on a pivot axis for-mounting said rudder on a vessel, said rudder blade having at its trailing part divergent side wall surface means, said rudder blade having its maximum cross-sectional width at said divergent side wall surface means, flow-guiding plate means extending laterally outwardly to either side of the rudder in planes transverse to said pivot axis whereby in use of the rudder the screw wash is confined against movement clear of the influence of the rudder in a vertical direction, said flow-guiding plate means intersect said divergent side wall surface defining means. 

1. A single-blade rudder secured to the stern of a ship for motion about a vertical pivot axis into opposite extreme or hardabout positions, the ship having a screw that generates a screw wash extending parallel to the forward direction of straight-line travel of the ship, the screw having a radius and a rotational outline, the rudder being situated in its entirety rearwardly of said screw in central alignment therewith, comprising in combination: a. a leading part extending from said pivot axis forwardly thereof and having a horizontally measured length dimension at least as large as the screw radius; and b. a trailing part extending from said pivot axis rearwardly thereof, said trailing part having
 1. a front portion extending from said pivot axis rearwardly thereof and having a horizontally measured length dimension at least as large as the screw radius, whereby a projection of said rotational outline of said screw onto said rudder parallel to said direction is substantially fully within the combined area of said leading part and said front portion of said trailing part in either extreme position of the rudder for receiving the entire screw wash, said leading part and said front portion of said trailing part effecting a first deflection of the screw wash;
 2. a rear portion adjoining a rear terminus of said front portion and extending rearwardly thereof, said rear portion including rearwardly divergent lateral wall surfaces for effecting a second deflection of the screw wash subsequent to its said first deflection when said rudder is in either of its extreme positions.
 2. A rudder as defined in claim 1, wherein said divergent wall surfaces of said rear portion are spaced from said pivot axis at a distance that is greater than said screw radius, whereby said divergent wall surfaces of said rear portion are situated externally of said projection Of said screw outline when said rudder is in either of said extreme positions.
 2. a rear portion adjoining a rear terminus of said front portion and extending rearwardly thereof, said rear portion including rearwardly divergent lateral wall surfaces for effecting a second deflection of the screw wash subsequent to its said first deflection when said rudder is in either of its extreme positions.
 3. A rudder as defined in claim 1, wherein the horizontally measured maximum distance between said divergent lateral wall surfaces constitutes the horizontally measured maximum cross-sectional width of the entire rudder.
 4. A rudder as defined in claim 1, wherein said leading part is formed of rearwardly divergent vertical wall surfaces, said front portion of said trailing part is formed of rearwardly convergent vertical wall surfaces.
 5. A rudder as defined in claim 1, wherein the ratio of the length dimension of said trailing part to the length dimension of said leading part is smaller than 2:1, said length dimensions are horizontally measured.
 6. A rudder as defined in claim 1, wherein said leading part has an extreme leading edge having a cutter-like configuration of a width substantially less than the mean blade width measured horizontally transversely to said direction.
 7. A rudder as defined in claim 6, said rudder having a central longitudinal vertical plane, said leading edge includes a strip of sheet metal extending in said plane.
 8. A rudder as defined in claim 1, wherein each of said divergent wall surfaces of said rear portion is formed by a free web plate.
 9. A rudder as defined in claim 8, wherein said web plates have an airfoil cross section with a rearwardly tapering outline.
 10. A rudder as defined in claim 8, including means defining throughflow slots between said outwardly projecting plates and said blade.
 11. A rudder as defined in claim 1, including flow-guiding plate means extending laterally outwardly to either side of the rudder in planes transverse to said pivot axis, said flow-guiding plate means intersect said divergent wall surfaces of said rear portion, whereby in use of the rudder the screw wash is confined against movement clear of the influence of the rudder in a vertical direction.
 12. A rudder as defined in claim 11, wherein said flow-guiding plate means extend in two vertically spaced planes each lying externally of said projection of said outline, said divergent wall surfaces of said rear portion are formed by free web plates projecting outwardly of the rudder blade and secured to said flow-guiding plate means.
 13. A marine single blade stern rudder comprising a rudder blade having leading and trailing parts, means for receiving a pivot shaft on a pivot axis for mounting said rudder on a vessel, said rudder blade having at its trailing part divergent side wall surface means, said rudder blade having its maximum cross-sectional width at said divergent side wall surface means, flow-guiding plate means extending laterally outwardly to either side of the rudder in planes transverse to said pivot axis whereby in use of the rudder the screw wash is confined against movement clear of the influence of the rudder in a vertical direction, said flow-guiding plate means intersect said divergent side wall surface defining means. 